Ethanol Production Process

ABSTRACT

An improved ethanol production process providing novel stillage treatment is disclosed wherein the stillage is separated into four value added product streams that are subjected to drying conditions reducing or eliminating volatization of any VOC&#39;s in the product streams.

PRIORITY STATEMENT

This is a Divisional of application Ser. No. 10/281,490 filed on Oct.28, 2002. The entire contents of which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to ethanol production processes, andmore particularly to ethanol production processes having enhanced valueproducts produced from the whole stillage and/or reduced volatileorganic compounds (VOC) emissions from the process.

2. Prior Art

In a conventional ethanol production process utilizing corn as thestarch containing feedstock, the corn is ground to produce a milledcorn. This is typically achieved by the use of a hammer mill or othersimilar conventional milling equipment Water and enzymes are added tothe milled corn and heated to form a liquefied mash. The liquefied mashis then mixed in a fermentation vessel with water, yeast and selectedminerals and nutrients to enhance the fermentation of the mash. Thefermented product, commonly referred to as the “beer”, is then distilledto produce an ethanol rich stream (about 95% ethanol and 5% water byweight) and a whole stillage. The whole stillage comprises water, aswell as the solids resulting from the fermentation. It is typical tocentrifuge the whole stillage to remove a substantial portion of thewater to form a wet distillers grain. The wet distillers grain includesmost of the protein containing solids that is found in the wholestillage. The removed water containing nutrients and other solidsgenerally known as the thin stillage is sent to an evaporator to removea substantial portion of the water. The remaining nutrients and solidscalled the syrup are then combined with the wet distillers grain. Thecombined syrup and wet distillers grain is sent to a dryer to produce adry protein containing animal feed called distiller dried grain solubles(DDGS).

These prior art ethanol processes have several significant problems. Oneproblem is the energy costs to remove the water from the whole stillageto produce a low economic value DDGS. A second problem is theenvironmentally unacceptable amount of VOC's, air toxics, and combustionpollutants, such as CO, NO_(x), and particulate matter, released intothe atmosphere during the drying process. To achieve an acceptable VOC,air toxics, and combustion pollutants release amount requires largecapital investments in thermal oxidizers and other equipment to capturethe VOC, air toxics, and combustion pollutants released during thedrying process, as well as expensive annual equipment maintenance. Theseproblems have hampered the commercial success of ethanol productionprocesses that have to date remained economically viable due only togovernmental subsidies.

OBJECTS AND SUMMARY OF THE INVENTION

Therefore, one object of this invention is to provide an improvedethanol production process that results in value added flavor enhancing,nutritional, nutraceutical, and/or pharmaceutical byproducts.

Another object of this invention is to provide an improved ethanolproduction process that minimizes the amount of VOC and other pollutantsreleased to the atmosphere during the treatment of the whole stillage.

Still another object of this invention is to provide an improved ethanolproduction process requiring reduced capital equipment investment andreduced maintenance costs.

Other objects and advantages of this invention shall become apparentfrom the ensuing descriptions of the invention.

Accordingly, an improved ethanol producing process is disclosed whereina starch-containing feedstock is hydrolyzed to produce ethanol and awhole stillage. The whole stillage comprises the remaining solids,nutrients, yeast and water remaining after the ethanol has been removedduring the hydrolysis step. The whole stillage is centrifuged, filteredor otherwise separated by other known techniques to produce wetdistillers grain and a thin stillage stream. The wet distillers grain,also known as thick stillage, includes most of the protein containingsolids and some of the water comprising the whole stillage. The thinstillage will comprise the nutrients, yeast and most of the water in thewhole stillage. The wet distillers grain is dried under conditions thatdo not denature the proteins contained in the thick stillage, and morepreferably, under conditions that minimize the volutizing of the VOCcontained in the wet distillers grain. The drying conditions depend on avariety of factors. When utilizing a spray dryer, these factors includethe ease in which the wet distillers grain can be atomized, the humidityof the air in the drying environment, the temperature of the hot airused to dry the wet distillers grain, the temperature of the wetdistillers grain when it enters the spray drier, and the contact timebetween the hot air and the atomized wet distillers grain. In apreferred embodiment these factors are controlled to produce a proteinrich product having a water content of less than about 15% by weight. Ithas been found that setting the temperature and contact time to achievea hot air exhaust temperature between about 140° F. and about 170° F.will result in a protein rich product containing less than about 15%water by weight and whose proteins have not been denatured. Under normalhumidity conditions and using a conventional spray dryer an exhausttemperature in the above range should result in an inlet hot airtemperature of less than about 450° F., and a contact time of less thanabout three minutes. Utilization of the above drying conditions willalso reduce the VOC emission to the atmosphere. In a preferredembodiment the drying conditions are set to maintain the temperature ofthe wet distillers grain below the temperature required to volatize mostof the VOC's. It is further preferred that any VOC that is volatizedpass through a cold trap and then filtered to remove water to produce aVOC product. The VOC product can then be utilized as a supplement toflavor enhance other products.

If desired the thin stillage stream can be sent to an evaporator toremove most of the water to produce the syrup. The syrup can be added tothe wet distillers grain prior to the drying step and be processed underthe same conditions as the wet distillers grain as described above.

In another alternate embodiment the thin stillage stream is passedthrough a microfiltration unit utilizing a filter size to form acarotenoid containing retentate and a nutrient rich permeate. A filterhaving a pore size of about 0.1 to 1.0 micron can be used. Thecarotenoid containing retentate is then dried to produce a carotenoidrich product having less than about 15% water by weight. It has beenfound that setting the temperature and contact time to achieve a hot airexhaust temperature between about 140° F. and about 170° F. will resultin a carotenoid rich product containing less than about 15% water byweight. Under normal humidity conditions and using a conventional spraydryer an exhaust temperature in the above range should result in aninlet hot air temperature of less than about 450° F., and a contact timeof less than about three minutes. In a preferred embodiment anyvolatized VOC is passed through a cold trap and filter to produce aliquefied VOC product.

In another alternate embodiment the nutrient rich permeate is passedthrough an ultrafiltration unit utilizing a filter size to form aprotein and yeast containing retentate and vitamin and mineralcontaining permeate. A filter having a pore size of less than about 0.1microns is preferred. The protein and yeast containing retentate isdried to produce a protein and yeast rich product having less than 15%water by weight. It has been found that setting the temperature andcontact time to achieve a hot air exhaust temperature between about 140°F. and about 170° F. will result in a protein and yeast rich productcontaining less than about 15% water by weight and whose proteins havenot been denatured. Under normal humidity conditions and using aconventional spray dryer an exhaust temperature in the above rangeshould result in an inlet hot air temperature of less than about 450°F., and a contact time of less than about three minutes. The vitamin andmineral containing permeate can also be dried under the same conditionsas the protein and yeast containing retentate to produce a vitamin andmineral rich product having less than 15% water by weight. It ispreferred that any volatized VOC's be passed to a cold trap and filterto produce a liquid VOC product.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate a preferred embodiment of thisinvention. However, it is to be understood that this embodiment is notintended to be exhaustive, nor limiting of the invention. They are butexamples of some of the forms in which the invention may be practiced.

FIG. 1 is a schematic illustrating a conventional prior art ethanolproduction process.

FIG. 2 is a schematic illustrating a preferred embodiment of thisinvention to treat the wet distillers grain to produce a non-denaturedprotein rich product.

FIG. 3 is a schematic illustrating a preferred embodiment of thisinvention to treat the thin stillage through use of microfiltration toproduce a carotenoid rich product.

FIG. 4 is a schematic illustrating a preferred embodiment of thisinvention to treat the permeate stream from the microfiltration throughuse of ultrafiltration to produce a protein/yeast rich product and/or avitamin/mineral rich product.

PREFERRED EMBODIMENTS OF THE INVENTION

Without any intent to limit the scope of this invention, reference ismade to the figures in describing the preferred embodiments of theinvention utilizing corn as the starch containing feedstock. The processdescribed herein can also be used with other starch containingfeedstocks such as bagasse, sugar cane, grains, and other starchcontaining materials.

In a conventional ethanol production process as illustrated in FIG. 1, astarch-containing feedstock 1, such as corn, is fed to a grinder 2 toproduce a milled corn 3. The milled corn 3 is then send to a mixer 4where water 5, as well as enzymes 6, are added to produce a liquid mash7. The liquid mash 7 is then sent to a fermentation vessel 8 where thedesired yeast and additional enzymes 9, as well as the minerals andnutrients 10 necessary for efficient fermentation, are added. After thedesired amount of fermentation has been completed the resulting product11 commonly referred to as the “beer” is sent to a distillation unit 12where an ethanol rich (about 95% ethanol by weight) stream 13 isseparated from the remaining fermented solids and water. The remainingfermented solids and water is generally known as the whole stillage 14.The whole stillage 14 is treated to produce an animal feed commonlyknown as DDGS. The most common method to treat the whole stillage 14 isto separate the whole stillage 14 by centrifuge 15 to form two separatestreams. The first is known as the wet distillers grain 16. The wetdistillers grain 16 includes most of the solids and some of the waterfound in the whole stillage 14. The second stream is known as the thinstillage stream 17. It includes the minerals, nutrients, yeast and theremaining water that was found in the whole stillage 14. In a typicalprocess the thin stillage stream 17 is sent to evaporator 18 where water19 is removed and the remaining solids or syrup 20 are combined with thewet distillers grain 16 and sent to a drum dryer 21. The dryer 21 istypically operated with the hot air having an inlet temperature at about1000° F.-1200° F. The hot air will remain in contact with the wetdistillers grain 16 and syrup 20 for approximately five minutes beforeexiting the dryer 20 having an exhaust temperature at about 200° F.-225°F. At these conditions the protein contained in the dried solids 24 aredenatured and are only good for use in animal feed known as DDSG. Inaddition any water vapor 22 and VOC 23 in the wet distillers grain 16and syrup 20 is volatized and either released to the atmosphere orpassed through expensive conventional thermal oxidizers (not shown).

The process of this invention involves improved treatment of the wholestillage 14 to produce products each having greater economic value thanDDGS, as well as significantly reduce the costs of treatment of theemissions from the process. In particular the amount of VOC emissionscan be reduced while at the same time producing a flavor enhancementsupplement product. Turning now to FIG. 2, the whole stillage 14 isagain separated into two product streams by centrifuge 15. Other knownseparating equipment such as filters could be used. These two streamsinclude the wet distillers grain 16 containing most of the proteincompounds found in the whole stillage 14 and the thin stillage stream 15containing most of the carotenoid, yeast, vitamin, mineral, andremaining protein compounds.

The wet distillers grain 16 is sent to spray dryer 21 that is operatedat conditions controlled to produce a protein rich product having awater content of less than about 15% by weight. It has been found thatsetting the temperatures of the hot air and the wet distiller grain 16,as well as their contact time to achieve a hot air exhaust temperatureof between about 140° F. and about 170° F. will result in the productionof a protein rich product 23 having a water content of less than about15% by weight. Under normal humidity conditions a hot air exhausttemperature in the above range would likely require an inlet hot airtemperature of less than about 450° F., and a contact time of less thanabout three minutes. Within these drying conditions the wet distillersgrain temperature should remain below the temperature to volatize most,if not all, of the VOC contained in the wet distillers grain. Thus, asignificant portion of the VOC will remain in the protein rich product23. This has the result of not only reducing the VOC that are volutized,but maintaining more of the flavor enhancing compounds in the proteinrich product 23. It is also preferred that the protein rich product 23be cooled upon leaving dryer 21 to prevent any further volutization ofthe VOC that is contained in the protein rich product 23. One method ofcooling the protein rich product 23 is through the use of a fluidizedbed wherein cool or ambient temperature air is used to fluidize the bed.Other known cooling techniques could be employed.

The water and any VOC vapor 22 removed during drying can be recycled tothe mixer 4. Depending on the dryer operating conditions some VOC may bevolatized. Because the volume of the volutized VOC is substantially lessthan in a conventional whole stillage treatment process, the water andVOC vapor 22 can be sent through a conventional and less expensive coldtrap 24 to produce a liquid VOC product 25. Water 26 in the liquid VOCproduct 25 can be removed, such as by filter 26 or other knownseparating equipment, to produce a dry VOC product 28 that can be soldas a flavor enhancing additive.

Turning now to FIG. 3 in another preferred embodiment the thin stillage17 is passed through a microfiltration unit 29 having a filter size ofabout 0.1 to 1.0 micron to form a retentate stream 30 and a permeatestream 31. In a more preferred embodiment the filter size is set tocapture in the retentate stream 30 the carotenoid compounds. Carotenoidcompounds, particularly Lutien and Zeaxantin, have been found useful inreducing various serious eye diseases such as age related maculardegeneration and cataracts. The retentate stream 30 containing thecarotenoid compounds is sent to dryer 32. In a preferred embodimentdryer 32 will be operated at a temperature to minimize the denaturing ofany protein contained in the retentate stream 30, as well as to preventvolatization of the VOC's in the retentate stream 30 during the periodthat the retentate stream 30 is contained in the dryer 32. This can beachieved if the retentate stream 30 is retained in dryer 32 for a periodof less than about three minutes, and the dryer 32 is operated with ahot air exhaust temperature less than about 170° F. to remove the water.Operated in this manner sufficient water can be removed to form acarotenoid rich product 34 having less than 15% water by weight.Depending on the dryer operating conditions and the retention time ofthe retentate stream 30 in the dryer 32 some VOC may be volatized.Because the volume of the VOC is substantially less than in aconventional whole stillage treatment process, the water and VOC vapor33 can be sent through a conventional and less expensive cold trap 35 toproduce a liquid VOC stream 36. Stream 36 can be recycled to mixer 4 orpreferably the liquid VOC can be separated from the water 38 in stream36 by a filter 37 to produce VOC product 39 that can be sold as a flavorenhancing additive.

Turning now to FIG. 4 in another preferred embodiment the permeate 31 ispassed through an ultrafiltration unit 40. The filter size is selectedto be less than about 100,000 molecular weight to produce a protein andyeast rich retentate 41 and a vitamin and mineral rich permeate 42. Theprotein and yeast rich retentate 41 is sent to dryer 43 to remove atleast a substantial portion of the water from the retentate 41. It ispreferred that the dryer 43 be operated to minimize the volalization ofany VOC's in the retentate 41. This can be achieved by utilizing thesame operating conditions as described above for dryer 32. Operated inthis manner sufficient water can be removed to form a protein and yeastrich product 45 having less than 15% water by weight. Depending on thedryer operating conditions and the retention time of the protein andyeast retentate 41 in the dryer 43 some VOC may be volatized. Becausethe volume of the VOC is substantially less than in a conventional wholestillage treatment process, the water and VOC vapor 44 can be sentthrough a conventional and less expensive cold trap 48 to produce aliquid VOC stream 49. Stream 49 can be recycled to mixer 4 or preferablythe water 51 in stream 41 can be separated by filter 50 to form a VOCproduct 52 that can be sold as a flavor enhancing additive.

In another preferred embodiment the vitamin and mineral rich permeate 42is sent to the dryer 46 to remove at least a substantial portion of thewater in permeate 42. It is preferred that the dryer 46 be operated tominimize the volalization of any VOC's in the permeate 42. This can beachieved by operating dryer 46 under the same conditions as dryer 43.Operated in this manner sufficient water can be removed to form avitamin and mineral rich byproduct 47 having less than 15% water byweight. Depending on the dryer operating conditions and the retentiontime of the permeate 42 in the dryer 46 some VOC may be volatized.Because the volume of the VOC is substantially less than in aconventional stillage treatment process, the water and VOC vapor can besent through a conventional and less expensive cold trap 48 to produce aliquid VOC stream similar to stream 49. This stream can also be recycledto mixer 4 or passed through a filter, such as filter 50, to form a VOCproduct that can be sold as a flavor enhancing additive.

Thus, as shown in the FIGS. 2-4, the whole stillage 14 can be processedto produce a protein rich product 23, a carotenoid rich product 34, aprotein and yeast rich product 45, and a vitamin and mineral richproduct 47 with minimum or no VOC's released to the atmosphere. TheVOC's produced do not have to be treated by expensive thermal oxidizersor similar equipment, but can be sent to a less expensive cold trap andfilter to produce yet another value added product, liquid VOC's. Each ofthese five product streams has significantly greater commercial valuethan the currently produced animal feed DDGS.

It is not necessary that separate cold traps be used for each of theproduct streams. Depending on the amount of VOC volatized, the differentVOC streams volatized can be combined and sent to one or more of thecold traps, thus further reducing capital expense. Depending on theproduct desired it is also possible to direct various streams to acommon dryer. There are of course other alternate embodiments that areobvious from the foregoing descriptions of the invention which areintended to be included within the scope of the invention as defined bythe following claims.

1. In an ethanol production process wherein a starch-containingfeedstock is hydrolyzed to produce ethanol and whole stillage, theimprovement to which comprises: (a) separating the whole stillage toproduce a protein-containing solids stream and a solubles stream, and(b) drying the protein-containing solids stream at a temperature lessthan required to denature protein contained in the protein-containingsolids stream and for a period of time to produce a protein rich producthaving a water content of less than about 15% by weight.
 2. The improvedprocess according to claim 1 wherein the protein-containing solidsstream is subjected to an inlet drying temperature less than about 450°F. and the period of time is less than about 3 minutes.
 3. The improvedprocess according to claim 2 wherein the protein rich product has aproduct temperature less than about 160° F. upon completion of thedrying.
 4. An improved process according to claim 1 further comprisingthe steps of: (a) filtering the solubles stream through a microfilter toform a carotenoid containing retentate and a nutrient containingpermeate, and (b) drying the carothenoid containing retentate for aperiod of time to produce a carothenoid containing product having awater content of less than about 15% by weight.
 5. The improved processaccording to claim 4 wherein the carotenoid containing retentate issubjected to an inlet drying temperature less than about 450° F. and theperiod of time is less than about 3 minutes.
 6. The improved processaccording to claim 4 further comprising the steps of: (a) filtering thenutrient containing permeate through an ultrafilter to form a proteinand yeast rich retentate and a nutrient rich permeate, and (b) dryingthe protein and yeast rich retentate for a period of time to produce aprotein and yeast rich containing product having a water content of lessthan about 15% by weight.
 7. In an ethanol production process wherein astarch-containing feedstock is hydrolyzed to produce ethanol and wholestillage, the improvement to which comprises: (a) separating the wholestillage to produce a protein-containing solids stream and a solublesstream, and (b) drying the protein-containing solids stream with hot airhaving a dryer inlet temperature less than about 450° F. for a period oftime to produce a protein rich product having a water content of lessthan about 15% by weight.
 8. The process according to claim 7 whereinthe VOC rich gaseous stream is processed through a cold trap to producea liquid VOC stream and the liquid VOC stream is treated to remove watercontained in the liquid VOC stream to form a VOC product.
 9. The processaccording to claim 7 further comprising the steps of: (a) filtering thesolubles stream through a microfilter to form a carotenoid containingretentate and a nutrient containing permeate, (b) filtering the nutrientcontaining permeate through an ultrafilter to form a protein and yeastrich retentate and a nutrient rich permeate, and (c) drying the proteinand yeast rich retentate for a period of time to produce a protein andyeast rich containing product having a water content of less than about15% by weight.
 10. The process according to claim 9 wherein the VOC richgaseous stream is processed through a cold trap to produce a liquid VOCstream and the liquid VOC stream is treated to remove water contained inthe liquid VOC stream to form a VOC product.
 11. In an ethanolproduction process wherein a starch-containing feedstock is hydrolyzedto produce ethanol and whole stillage, the improvement to whichcomprises: (a) separating the whole stillage to produce aprotein-containing solids stream and a solubles stream, and (b) dryingthe protein-containing solids stream at a temperature less than requiredto denature protein contained in the protein-containing solids and lessthan required to volatize the organic compounds contained in theprotein-containing solids for a period of time to produce a protein richproduct containing VOCs having a water content of less than about 15% byweight.
 12. In an ethanol production process wherein a starch-containingfeedstock is hydrolyzed to produce ethanol and whole stillage, theimprovement to which comprises: (a) separating the stillage to produce aprotein-containing solids stream and a solubles stream, (b) passing thesolubles stream through a microfilter to produce a carotenoid richretentate and a permeate, (c) passing drying the carotenoid richretentate at a temperature less than about 450° F. and for a period oftime to produce a carotenoid rich product having a water content of lessthan about 15% by weight.
 13. The process according to claim 12 furthercomprising passing any VOC released during drying through a cold trap toproduce a liquid VOC stream and the liquid VOC stream is treated toremove water contained in the liquid VOC stream to form a VOC product.14. The process according to claim 12 wherein the temperature is lessthan required to volatize at least some of any organic compoundscontained in the carotenoid rich retentate.
 15. In an ethanol productionprocess wherein a starch-containing feedstock is hydrolyzed to produceethanol and whole stillage, the improvement to which comprises:separating the stillage to produce a protein-containing solids streamand a solubles stream, (a) separating the stillage to produce aprotein-containing solids stream and a solubles stream. (b) passing thesolubles stream through a microfilter to produce a carotenoid richretentate and a permeate; (c) passing the permeate through anultrafilter to produce a protein and yeast rich retentate and a nutrientrich permeate, (d) drying the protein and yeast rich retentate at atemperature less than about 450° F. and for a period of time to producea protein and yeast rich product having a water content of less thanabout 15% by weight.
 16. The process according to claim 15 furthercomprising passing any VOC released during drying through a cold trap toproduce a liquid VOC stream and the liquid VOC stream is treated toremove water contained in the liquid VOC stream to form a VOC product.17. The process according to claim 15 wherein the temperature is lessthan required to volatize at least some of any organic compoundscontained in the protein and yeast rich retentate.
 18. The processaccording to claim 15 further comprising drying the nutrient richpermeate at a temperature less than about 450° F. and for a period oftime to produce a vitamin and mineral rich product having a watercontent of less than about 15% by weight.
 19. The process according toclaim 18 further comprising passing any VOC released during drying ofthe nutrient rich permeate through a cold trap to produce a liquid VOCstream and the liquid VOC stream is treated to remove water contained inthe liquid VOC stream to form a VOC product.
 20. The process accordingto claim 18 wherein the temperature is less than required to volatize atleast some of any organic compounds contained in the vitamin and mineralrich retentate.
 21. In an ethanol production process wherein astarch-containing feedstock is hydrolyzed to produce ethanol and wholestillage, the improvement to which comprises: (a) separating thestillage to produce a protein-containing solids stream and a solublesstream, (b) passing the solubles stream through a microfilter to producea carotenoid rich retentate and a permeate, (c) passing the permeatethrough an ultrafilter to produce a protein and yeast rich retentate anda nutrient rich permeate, and (d) drying the nutrient rich permeate at atemperature less than about 450° F. and for a period of time to producea vitamin and mineral rich product having a water content of less thanabout 15% by weight.
 22. The process according to claim 21 furthercomprising passing any VOC released during drying of the nutrient richpermeate through a cold trap to produce a liquid VOC stream and theliquid VOC stream is treated to remove water contained in the liquid VOCstream to form a VOC product.
 23. The process according to claim 21wherein the temperature is less than required to volatize at least someof any organic compounds contained in the vitamin and mineral richretentate.